1. Field of the Invention
The present invention relates to a method for retaining a stack of sheets in a post-processing unit. The present invention further relates to an apparatus for retaining a stack of sheets. The present invention further relates to a clip element for retaining a stack of sheets.
2. Description of Background Art
In a known post-processing unit, a finishing device is provided for automatically binding or clamping a stack of sheets together. The known finishing device contains a stapling unit for applying a staple, which is taken from a staple storage enclosure, onto the stack of sheets, and further contains a clip fitting unit for applying a clip, which is taken from a clip storage enclosure, onto the stack of sheets. The operator can choose whether the stack of sheets is to be stapled or to be clipped. In the known printing system, the shape of the staple element and clip element is restricted to the ones which are provided in the staple storage enclosure and the clip storage enclosure. Regularly, only one shape is provided in each of the storage enclosures of the finishing device; a conventional staple element is provided having a shape for providing a common binding distance and a conventional clip element is provided having a conventional clip shape for common use. However, if a stack of sheets varies in certain aspects, such as thickness and surface properties, a selection of another shape for a staple element and a clip element is desirable in order to optimize binding strengths, ease of use of the binding element and reusability of the sheets of the stack.